docs: Update guides for Quill Editor and ActiveAdmin 4.0.0.beta20

- Replace Tom Select references with Quill Editor
- Update all version references to beta20
- Remove irrelevant guides (Tom Select migration, CKEditor upload system)
- Add Quill Editor specific imports and configurations
- Update package.json dependencies to use Quill instead of Tom Select

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/activeadmin-tailwind-4.md

@@ -1,8 +1,12 @@
 # ActiveAdmin + Tailwind CSS v4 Guide
 
-This guide consolidates the ActiveAdmin 4.0.0.beta19 upgrade notes with a working Tailwind v4 build setup. Use it as a template when updating other ActiveAdmin extension gems.
+This guide consolidates the ActiveAdmin 4.0.0.beta20 upgrade notes with a working Tailwind v4 build setup. Use it as a template when updating other ActiveAdmin extension gems.
 
-## What Changed in ActiveAdmin 4.0.0.beta19 (from UPGRADING.md)
+## What Changed in ActiveAdmin 4.0.0.beta20 (from UPGRADING.md)
+
+### Version Requirements
+- Rails 7.2+ (Rails 7.0 and 7.1 are no longer supported)
+- Ruby 3.2+ (Ruby 3.0 and 3.1 are no longer supported)
 
 ### Template Updates
 - `_site_header.html.erb` container class changed from `sticky` to `fixed`.
@@ -47,12 +51,19 @@ Tailwind config now uses ESM. To avoid the warning:
 - Deeply nested submenus removed (only one level supported).
 - Removed `Panel#header_action` and `index_column`.
 
+### New in beta20
+- Parent menu item linking support
+- Improved comments pagination styling
+- Better vertical spacing for has-many forms
+- Pointer cursor restored on eligible buttons
+- Various accessibility improvements
+
 ## Recommended Build Setup (tailwindcss-rails)
 
 ### 1. Gemfile
 
 ```ruby
-gem "activeadmin", "4.0.0.beta19"
+gem "activeadmin", "4.0.0.beta20"
 gem "tailwindcss-rails", "~> 4.4.0"
 ```
 
@@ -81,9 +92,9 @@ export default {
     `${activeAdminPath}/plugin.js`,
     `${activeAdminPath}/app/views/**/*.{arb,erb,html,rb}`,
     "./app/admin/**/*.{arb,erb,html,rb}",
-    "./app/views/active_admin/**/*.{arb,erb,html,rb}",
-    "./app/views/admin/**/*.{arb,erb,html,rb}",
-    "./app/views/layouts/active_admin*.{erb,html}",
+    "./app/views/active_admin/**/*.{arb,erb,html,rb}`,
+    "./app/views/admin/**/*.{arb,erb,html,rb}`,
+    "./app/views/layouts/active_admin*.{erb,html}`,
     "./app/javascript/**/*.js"
   ],
   darkMode: "selector",